Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Details Textual)

v2.4.0.8
Commitments and Contingencies (Details Textual) (USD $)
3 Months Ended 6 Months Ended
Nov. 30, 2013
May 31, 2013
Nov. 30, 2013
Line of Credit [Member]
Nov. 30, 2013
Revolving Credit Facility [Member]
Aug. 31, 2013
Revolving Credit Facility [Member]
Nov. 30, 2013
Revolving Credit Facility [Member]
Nov. 30, 2013
Standby Letters of Credit [Member]
May 31, 2013
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]                
Maximum amount outstanding during period       $ 175,000,000 $ 25,000,000      
Interest rate on amount borrowed       3.25% 3.25%      
Maximum borrowing capacity       500,000,000   500,000,000    
Expiration date           Jun. 21, 2018    
Amount outstanding     0 0   0    
Amount available             35,500,000 36,800,000
Expiration date range of letters of credit             July 2014 and December 2014  
Irrevocable stand by letters of credit amount outstanding             0  
Commitments and Contingencies (Textual)                
Commitments to purchase capital assets $ 6,400,000 $ 9,900,000